In screening of drugs that is executed in a pharmaceutical industry or the like, cells of animals or plants, microorganisms, or others are fed with a drug subject to the screening under various conditions and cultured, and their changes with time are observed for verification of efficacy of the drug. To verify efficacy of anticancer drug, for example, examining the degree of cancer cell-induced neovascularization, that is, the degree of growth of a newly branching capillary is often observed. The more active this neovascularization is, the more active the proliferation of the cancer cell. The anticancer drug is verified effective if the neovascularization is stopped or slowed by the administrated drug. In conventional observation of this neovascularization, length and area of the neovascularization are extracted, as an index of the neovascularization, from a microscopic image of a living sample, and the degree of neovascularization is determined based on the index.
In the process of the neovascularization, the capillary grows while keeping branching out. To accurately ascertain the degree of neovascularization, it must be determined how the capillary branches out.
In the microscopic image, the capillaries form a complex, random line pattern including plural combinations of line elements having irregular shapes. In the conventional screening of the drugs that uses the length and area of the neovascularization as an index, the branching random line pattern cannot be extracted as actual data. Consequently, the degree of neovascularization is hardly determined.